The present invention relates to internal combustion engines and in particular to a crankless over-expanded variable-compression engine with regenerative internal-cooling using constant-volume combustion and rotary-valves.
The thermodynamic efficiency of an internal combustion engine is strongly related to a compression ratio of the engine. Typical automotive engines have compression ratios of 8.5:1 to 12:1 for street driven automobiles, and sometimes higher for racing engines using special racing fuel in racing conditions. Higher compression ratios for street driven automobiles would increase the thermodynamic efficiency, and thus the gas mileage, but also results in detonation in the combustion chambers of the engines resulting in damage and eventual failure.
The energy distribution chart for a conventional four stroke, Spark Ignition (SI) engine, is about 30 percent usable work, 35 percent into the cooling system (which includes heat generated by friction between moving parts), and 35 percent goes out the exhaust. The first 30 percent corresponds to the engine's overall efficiency, and based on this value, one may assume that it's running at Wide Open Throttle (WOT). Internal Combustion Engines (ICE) are theoretically less efficient at partial throttle settings then when running wide open due to parasitic losses, etc.
Thermodynamic theory suggests, that a heat engine of this type may achieve an efficiency factor of about 60-65 percent at best, but known engines are far from that, and 70 percent of the energy available in a gallon of gasoline is wasted. Automobile manufacturers continue their efforts to improve the situation, and they have been succeeding, as the average miles per gallon has been steadily rising. Improvements include reducing vehicle weight, better aerodynamics, operating hybrid engines at their most efficient speeds, turbo chargers to recapture some of the exhaust's wasted heat, and engines running with higher compression ratios and therefore, more thermodynamically efficient. However, these small incremental changes have become few and far between and more costly.
Known four stroke, spark ignited engine include a series of pistons, in a line, move up and down in cylinder sleeves capped by a header. The pistons connect to a crankshaft, via connecting rods, which controls the piston's motion (stroke). In a first stroke (intake), the crankshaft pulls the piston down, from Top Dead Center (TDC) creating a vacuum inside the corresponding cylinder, and with the intake valve open, draws an Air/Fuel Mixture (AFM) into the cylinder. At Bottom Dead Center (BDC) the cylinder is at its largest volume and the intake valve closes trapping in the ingested AFM. Next, the piston starts up on the second stroke (compression) back to TDC. The compression stroke compresses and heats the AFM according to the physical parameters of the engine. Since the piston's up and down strokes are controlled by the crankshaft, they are all exactly the same length, and the compression ratio is set as a fixed value during the engine's design phase. Compressing the AFM takes a large amount of energy which reduces the power output. To get the maximum amount of energy out of known engines, the AFM half burn must be completed by about 10 degrees of crankshaft rotation after TDC and ignition must take place from 10 to 60 degrees before TDC because the fuel burn takes 20 to 70 degrees of crankshaft rotation to complete. So the AFM is burning before TDC and is getting hotter and pressure in the cylinder is rising over and above that caused by the compression process itself, which increases the negative work.
The third stroke (expansion or power) begins after TDC of the compression stroke. Gas engines are limited in the compression ratio because of a phenomenon called detonation or knock. Detonation occurs because the compression ratio is so high and the combustion chamber wall so hot that the self-ignition temperature of the AFM is reached causing combustion. These are untimed events that often seriously damage the engine. The fourth and final stroke is the exhaust stroke. During the exhaust stroke, upward movement of the piston pushes engine exhaust out through the open exhaust valve. The power stroke is the only stroke which produces mechanical energy, and energy remaining in the cylinder at the end of the power stroke is lost as heat into the exhaust gases.
In summary, most of the energy in a gallon of gasoline is wasted. Even an ideal known SI engine will only recover another third of the energy in the gasoline burned by the engine, two revolutions of the crankshaft are required to produce ½ revolution of power, the piston strokes (all of them) are of equal and fixed length, wasting energy remaining in the cylinder at the end of the power stroke, and higher compression ratios which provide greater thermodynamic efficiency are not possible due to detonation.